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Earliest western references: “On Agriculture” by Marcus Terentius Varro (c. 36 BC): “...and because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases.”

“… nearly all the deaths had taken place within a short distance of the [Broad Street] pump… only ten deaths in houses situated decidedly nearer to another street-pump. In five of these … they always sent to the pump in Broad Street…. In three other cases, the deceased were children who went to school near the pump in Broad Street... With regard to the deaths occurring in the locality belonging to the pump, there were 61 instances in which I was informed that the deceased persons used to drink the pump water from Broad Street, either constantly or occasionally...

The result of the inquiry, then, is, that there has been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above-mentioned pump well.

I had an interview with the Board of Guardians of St James's parish, on the evening of the 7th inst [Sept 7], and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day.

~1590, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, while experimenting with several lenses in a tube, discovered that nearby objects appeared greatly enlarged.

1609, Galileo, … heard of these early experiments, worked out the principles of lenses, and made a much better instrument with a focusing device.

Anton van Leeuwenhoek (1632-1723) …taught himself new methods for grinding and polishing tiny lenses of great curvature … magnifications up to 270 diameters, … He was the first to see and describe bacteria, yeast plants, the teeming life in a drop of water, and the circulation of blood corpuscles in capillaries.

Robert Hooke, the English father of microscopy, re-confirmed Anton van Leeuwenhoek's discoveries of the existence of tiny living organisms in a drop of water. Hooke made a copy of Leeuwenhoek's light microscope and then improved upon his design.

… "I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily a-moving. … The biggest sort. . . had a very strong and swift motion, and shot through the water (or spittle) like a pike does through the water. The second sort. . . oft-times spun round like a top. . . and these were far more in number."

… the Society appointed two scientists - Nehemiah Grew, the plant anatomist and Robert Hooke, the microscopist. First time they failed, casting doubts on his report. However, Hooke again tried using a microscope with 330 X (power of magnification) and confirmed Leeuwenhoek’s success. Both scientists confirmed that their observations were similar to those described in the letters by Leeuwenhoek.

Now, the Royal Society accepted Leeuwenhoek as scientist and declared him as the discoverer of bacteria.

Dmitri Ivanovsky (1892) tobacco mosaic disease, … was clearly infectious; …Hoping to find bacteria Ivanovsky ran extract of diseased leaves through filter, … pores small enough to trap any known bacteria…caused ….went right through …liquid retained the power to infect other plants.

Ivanovsky published findings… little attention was paid …

Martinus Beijerinck (1898) … same experiments … same results

infectious agent destroyed when the liquid was heated.

Beijerinck concluded agent was a "contagious living fluid."

Beijerinck (as Jenner) used the term "virus" (Latin for poison or pestilence.

hoof-and-mouth disease, yellow fever, … were also caused by these "filterable viruses."

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1930s filters with pores tiny enough to prove that viruses are particulate after all, rather than being fluid in nature.

The earliest electron microscopes also appeared in the 1930s, and viruses could at last be seen.

Today we know that viruses are not living cells like bacteria, but rather tiny packets of genetic material that must infect the cells of their unwilling host in order to reproduce.

Transmission to humans occurs through ingesting contaminated water or food

The major cholera pandemics are generally listed as: First: 1817-1823, Second: 1829-1851, Third: 1852-1859, Fourth: 1863-1879, Fifth: 1881-1896, Sixth: 1899-1923: Seventh: 1961- 1970, and some would argue that we are in the Eighth: 1991 to the present. Each pandemic, save the last, was accompanied by many thousands of deaths. As recently as 1947, 20,500 of 30,000 people infected in Egypt died. Despite modern medicine, cholera remains an efficient killer.